I have a feeling that OTS automatically enables sync start and you can't do anything about that.
From the Genos owner's manual (and same applies to all the arrangers)
"Not only does this instantly call up all the settings (Voices, effects, etc.) that match and are most commonly used with the current Style, it also automatically turns on ACMP and SYNC START, so that you can immediately start playing the Style."
You will need to use registrations if you want to set up style + voices without starting the accompaniment. Not as convenient as OTS to be sure, but it will then do what you want.